Wood-tar, under the title of Pix liquida, is included in the pharmacopoeia, in which its character is given as follows: "Thick, viscid, brownish-black, of a well-known peculiar aromatic odor. Water agitated with it acquires a pale-brown color, sharp, em pyreumatic taste, and acid reaction." Tar was more used in medicine in former times than at present. Bishop Berkeley's commendatory essay on the use of tar-water in dis eases of the chest and kidneys, is well known to all literary students. (See Chambers' Book of Days, vol. i. p. 108.) Since his time the inhalation of tar-vapor has been highly recommended in cases of pbthisis; and tar capsules are still occasionally prescribed in cases of relaxed mucous membrane. In the present day, tar is, however, seldom used except as a local stimulant in chronic cutaneous diseases.
In modern commerce there are two kinds of wood-tar known—that made in the north of Europe from the wood of Perms sylvestris, and the North American, which is made from Pinus rigida, P. Ueda, P. Australis, &c. The distillation is usually performed in a very rude manner: a funnel-shaped hole is dug in a bank, about 6 or 8 ft. in diameter at the upper part, and not more than 18 in. at the lower. At the bottom of the hole
is placed an iron pan, having a long spout or pipe, which is made to pass through the bank; the hole is then filled up with billets cut from the roots and branches of the pine trees, which, after being kindled at the top, are covered over completely with turf. The wood is thus charred from above downward; and the tar, mixed with various other pro ducts, flows off at the nottom through the spout into a receiver. A somewhat similar product is obtained in the distillation of coal for gas, and in the distillation of bones in forming animal charcoal. Formerly, the chief value of these materials was as a preserv ative coating for exposed wood-work, ships' sails, ropes, &c., in consequence of their very highly antiseptic properties. A better knowledge of their chemical history has, however, mach increased their value. The imports of wood-tar into Great Britain ex ceed five millions of gallons annually; while the supply of coal-tar produced in the gas works, charcoal-works, and bone-works of the United Kingdom cannot be estimated at much under that quantity.